1. Field
The present disclosure relates to low-defect semiconductor devices and methods of manufacturing the same, and more particularly, to small-sized semiconductor devices with reduced twist grain boundary generation, and methods of manufacturing the same.
2. Description of the Related Art
Sapphire substrates or silicon carbide (SiC) substrates are widely used to manufacture nitride-based semiconductor devices. However, the sapphire substrates have low electrical conductivity, and are unsuitable for chip fabrication because they are expensive and hard. Also, when the sapphire substrates are epitaxially grown to have a large diameter, they warp at a high temperature due to their low thermal conductivity. Therefore, it is difficult to fabricate large-area sapphire substrates. In order to overcome these limitations, nitride-based semiconductor devices fabricated by using silicon substrates instead of sapphire substrates have been developed.
Since the silicon substrates have higher thermal conductivity than the sapphire substrates, they warp only a little even at a high temperature, at which a nitride thin film grows, and thus, may grow to have a large diameter. However, when a nitride thin film is grown on a silicon substrate, a dislocation density (or defect density) increases due to a lattice constant mismatch between the silicon substrate and the thin film and a crack occurs in the silicon substrate due to the thermal expansion coefficient mismatch therebetween. Therefore, methods for reducing such a dislocation density and methods for preventing such a crack have been extensively researched. However, when the dislocation density is reduced, a tensile stress occurs incidentally. Therefore, when the dislocation density is reduced, the crack occurrence is increased. On the other hand, when the crack occurrence is reduced, the dislocation density is increased. Thus, it is difficult to reduce both the dislocation density and the crack occurrence when the nitride thin film is grown on the silicon substrate.